Dual connectivity is an operation where a given UE consumes radio resources provided by at least two different network points (Master and Secondary eNBs) connected with non-ideal backhaul. RAN2 has agreed the control plane architecture for dual connectivity is C1: Only the MeNB generates the final RRC messages to be sent towards UE after the coordination of RRM functions between MeNB and SeNB, and UE only sends a RRC message to the MeNB. The user plane architecture is 1A and 3C. Readers can refer to TR36.842 for the details for architecture 1A. Architecture 1A refers to that a bearer severed by the SeNB and its user plan radio protocols (including PDCP, RLC and MAC) are all in the SeNB.
When architecture 1A is applied, for the bearers severed by the SeNB, PDCP entity is located in the SeNB, and PDCP entity is responsible for the encryption. Therefore, in the architecture 1A situation, there will two security keys for the MeNB and SeNB, respectively. In the present standards, only one single security key is provided for UE by the network. As described above, in the situation for a user plane architecture 1A based dual connectivity, it is also necessary to refresh the key. Therefore, the problem that how to refresh the key in the dual connectivity situation has not been solved yet.